1. Field of the Invention
The present invention relates to a magnetic sensor device for converting a magnetic field intensity into an electric signal, and for example, to a magnetic sensor device to be employed as a sensor for detecting an open/close state used in a flip phone, a notebook computer, or the like, or a sensor for detecting a rotational position of a motor.
2. Description of the Related Art
A magnetic sensor device has been employed as a sensor for detecting the open/close state used in a flip phone, a notebook computer, or the like, or a sensor for detecting a rotational position of a motor.
In the magnetic sensor device, a magnetoelectric conversion element (for example, Hall element) outputs a voltage proportional to a magnetic field intensity or a magnetic flux density, an amplifier amplifies the output voltage, and a comparator determines the voltage to output a binary signal of an H signal or an L signal. The output voltage of the magnetoelectric conversion element is minute, and hence, easily affected by an offset voltage (element offset voltage) of the magnetoelectric conversion element, an offset voltage (input offset voltage) of the amplifier or the comparator, or noise within a conversion device, which leads to a problem. The element offset voltage is mainly generated by a stress or the like exerted on the magnetoelectric conversion element by a package. The input offset voltage is mainly generated by a characteristic variation of an element that forms an input circuit of the amplifier. The noise is mainly generated by flicker noise of a monolithic transistor that forms a circuit, or thermal noise of the monolithic transistor or a resistive element.
There has been devised a magnetic sensor device which reduces an influence of the above-mentioned offset voltage of the magnetoelectric conversion element or the amplifier (for example, see Japanese Patent Application Laid-open No. 2010-281801). A conventional magnetic sensor device illustrated in FIG. 3 includes a Hall element 51 serving as a magnetoelectric conversion element, a switching circuit 52, a differential amplifier 53, a comparator 54, a detection voltage setting circuit 55, a first capacitor C51 and a second capacitor C52, and a first switch S51 and a second switch S52.
FIG. 4 illustrates a timing chart of the operation of the conventional magnetic sensor device. One period T of the detection operation is divided into a first detection state T1 and a second detection state T2 depending on the operation of the switching circuit 52. In the first detection state T1, a first pair of terminals A and C of the Hall element 51 inputs a power supply voltage, and a second pair of terminals B and D outputs a detection voltage. In the second detection state T2, the second pair of terminals B and D inputs the power supply voltage, and the first pair of terminals A and C outputs the detection voltage. One period T is further divided into a first sample phase F1, a second sample phase F2, and a comparison phase F3 depending on the open/close states of the respective switches. Then, in the comparison phase F3, offset components are removed.
In the conventional magnetic sensor device, however, the detection voltage setting circuit 55 formed of a bleeder resistor is required to be provided in order to set a detection voltage level for the magnetic field intensity, resulting in the complicated circuit configuration. Further, different power supply systems are necessary for the Hall element 51 and the detection voltage setting circuit 55, resulting in a problem in that an error occurs in the setting of the detection voltage level. Still further, as described above, the total of three signal processing periods, two sample phases and one comparison phase, are necessary for removing the offset components.